Theory of many-body effects on conduction-electron spin resonance in anisotropic metals

We present the details of an earlier Letter in which we showed that many-body effects qualitatively change the behavior of conduction-electron spin resonance (CESR) in metals having a spread in $g$ values over the Fermi surface. When scattering is too slow to motionally narrow CESR we show that electron correlations and $g$ anisotropy combine and lead to an exchange-narrowed collective mode. This mode is Lorentzian and its width would vanish in the absence of scattering. The position of the collective mode is shifted from the position of the motionally narrowed CESR which one would observe at high temperatures. This shift offers the possibility of determining the electron-electron exchange interaction in metals for which spin waves have not yet been observed. We discuss the behavior of CESR in general and derive equations for the linewidth and resonance position in one interesting limit.